The present invention relates to an illumination apparatus for a microscope in which the diameter of an aperture diaphragm or the like is switched in association with switching of an observation method or an objective lens.
In an illumination (an incident illumination, a projection illumination) observation microscope, illumination light radiated from an illumination light source is passed through an objective lens and irradiated onto a sample. Reflection light from the sample is passed through the objective lens again so as to enter into an eyepiece lens or a television camera, thus achieving observation. In this microscope, a plurality of objective lenses are attached to a revolving nosepiece (revolver), and observation can be performed while changing the magnification by rotating the revolving nosepiece.
Recently, in many revolving nosepieces of this type, objective lenses are changed from each other by electrically rotating the revolving nosepiece. There are also microscopes in which other various operating sections are electrified in addition to the revolving nosepiece so that operation is facilitated. In particular, if the aperture diaphragm and the field diaphragm in the illumination system are set to appropriate diaphragm diameters in compliance with the objective lens and in accordance with a bright field illumination observation method or a dark field illumination observation method, the optical performance can be extracted at maximum. Therefore, there has been provided a microscope which changes the diaphragm diameter under electric control in association with the revolving nosepiece.
For example, the aperture diaphragm and the field diaphragm in the bright field illumination observation takes various optimum diameters depending on the magnifications of the objective lenses and the pupil diameter. Therefore, control is performed so as to change the diaphragm diameters every time when the revolving nosepiece is switched. In addition, the aperture diaphragm and the field diaphragm in the dark field illumination observation are basically set to the maximum diameters, i.e., released in order to maximum use of the illumination light. These diaphragms are automatically switched to the maximum diameters when the dark field illumination is carried out.
FIGS. 15A and 15B are partial cross-sectional views showing a revolving nosepiece and an objective lens in the dark field illumination described above. FIG. 15A shows a light passage of illumination light for normal dark field illumination. The revolving nosepiece 301 is equipped with an objective lens 303 having a ring-like dark field illumination light passage 302. When dark field illumination light 305 enters into a dark field illumination light passage 304, this light 305 passes through the dark field illumination light passage 302 of the objective lens 303 and is irradiated onto a sample 306. At this time, regular reflection light from the sample 306 is reflected at the same angle as the incident angle to the sample 306, and therefore does not enter into the observation light passage 307 of the objective lens 303. Accordingly, only scattered light from the sample 306 enters into the observation light passage 307, so that an effective dark field illumination observation method can be practiced by detecting feeble scattered light.
However, a problem of stray light occurs when the revolving nosepiece 301 is rotated to change the objective lens 303. FIG. 15B shows a light passage for illumination light halfway while the objective lens 303 is changed with another one. That is, the revolving nosepiece 301 starts rotating to change the objective lens 303, and the objective lens 303 is slightly inclined and deviates from its original optical axis. In this situation, a part (in form of a crescent moon) of the ring-like dark field illumination light 305 comes out of the range of the dark field illumination light passage 302 of the objective lens 303, and passes through the observation light passage 308 of the objective lens 303, to be irradiated onto the sample 306. Further, the regular reflection light from the sample 306 enters into the observation light passage 307 of the revolving nosepiece 301 while maintaining its large amount, so that unnecessary excessive light beams as stray light enter.
Normally, dark field observation is carried out by detecting feeble scattered light, so the light amount of the illumination light is large while the observation light is weak. Therefore, if a large amount of stray light enters into the observation light passages 307 and 308 even at an instant halfway while changing the objective lens 303, an observer takes a risk for eyes of his or her own and feels dazzled in case of eye observation, and bad influences may be effected on the image pick-up element in case of television observation.
With respect to the problem as described above, for example, a conventional apparatus adopts a method of inserting and then pulling out a special shutter at the same time when an objective lens is changed. However, in this case, it is necessary to use a special shutter mechanism and other components which are disadvantageous in view of costs.
In contrast, in place of using such a shutter, there is a method of electrically reducing the field diaphragm to the minimum diameter by means of an iris diaphragm (a plurality of diaphragm wings) to prevent stray light at the same time when changing an objective lens. In this case, however, thin iris diaphragm must be opened and closed every time when an objective is changed, so that the durability of the iris diaphragm may become unreliable. In addition, the speed at which the iris diaphragm is limited by the unreliableness of durability caused due to opening and closing of the iris diaphragm, and as a result, it takes a very long time to change an objective lens.
As a known example, Japanese Patent Application KOKAI Publication No. 6-337359 discloses that the power source of an illumination light source is shut off to prevent stray light when changing an objective lens. Further, Japanese Patent Application KOKAI Publication No. 7-209584 discloses that a revolving nosepiece is rotated after the light amount drops sufficiently when changing an objective lens.
Although this technique brings about an effect that a large amount of stray light is prevented from entering into observation light passages, the illumination light source is turned on and off so frequently that the lifetime of the illumination light source is shortened as a result. For example, in case of a halogen lamp generally used as an illumination light source, it has been known that the lifetime is shortened if it is repeatedly turned on and off. In addition, many light sources cannot be turned on and off simply (e.g., ark light sources such as mercury lamps and the like). If one of those light sources is used, stray light cannot be prevented from entering, by turning on and off the lamps. Further, each of the techniques described above adds another operation to various switching operations, so that only a low efficiency can be attained in view of the electric power and the durability.
There is another known technique in which a light reduction unit based on adjustment of the brightness of a light source or based on switching of an ND filter (Neutral density filter) is electrically controlled in accordance with the magnification and the transmittance of the objective lens, thereby to minimize the change of the brightness caused by switching (or changing) an objective lens. These functions are optionally and selectively equipped in compliance with the use frequency and the price range.
Japanese Patent Application KOKAI Publication No. 9-21957 discloses a microscope in which the aperture diaphragm and the light adjustment unit (or ND unit) are controlled to attain optimum conditions on the basis of various original data concerning objective lenses. Objective lenses have respectively different transmittance depending on the magnifications and the numerical apertures (NA). In general, an objective lens having a high magnification has a low transmittance (dark) while an objective lens having a low magnification has a high transmittance (bright). It is considered that the aperture diaphragm for extracting the maximum performance of an objective lens should appropriately be set to about 70% relative to the pupil diameter of each objective lens. In this case, the pupil diameter of an objective lens having a high magnification is small while the pupil diameter of an objective lens having a low magnification is large.
From the above, it is known that an objective lens having a high magnification has a low transmittance and the diameter of the aperture diaphragm thereof must be reduced. Therefore, the efficiency of illumination is low and an observed image becomes dark. An objective lens having a low magnification has a high transmittance and the diameter of the aperture diaphragm thereof is therefore large. Therefore, an observed image becomes bright. Also, as for a predetermined objective lens, the diameter of the aperture diaphragm is reduced to decrease the numerical aperture so that the depth of the image is improved, or the aperture diaphragm is used to emphasize the contrast.
The microscope disclosed in Japanese Patent Application KOKAI Publication No. 9-21957 extracts the maximum optical characteristics of every objective lens, and at the same time, corrects differences in brightness between objective lenses by a ND unit. An operator is capable of making an observation with equal brightness for each objective lens.
However, in case where an objective lens is switched or changed, there is a problem that an observed image is felt dazzling for an observer if the observed image has excessive brightness at an instant or more even while switching an objective lens. This problem must be avoided. For example, when switching an objective lens having a high magnification to an objective lens having a low magnification, care must be taken that an observed image having unnecessarily high brightness is not viewed by the observer at an instant.
Against the problem described above, a known example adopts a manner that a special shutter is inserted and pulled off when an objective lens is switched. Therefore, a shutter mechanism and components are required so that the structure is disadvantageous in view of costs. Also, as described previously, Japanese Patent Application KOKAI Publication No. 6-337359 discloses a microscope illumination apparatus by which the power source for an illumination light source is shut off to prevent stray light when an objective lens is switched. Further, as a similar technique, Japanese Patent Application KOKAI Publication No. 7-209584 previously described discloses a microscope control apparatus which rotates its revolving nosepiece after having waited for an enough drop of the light amount. These proposals, however, involve the problems described above.
In case of appropriately adjusting the aperture diaphragm in a predetermined objective lens, the observed image becomes dark as the aperture diaphragm is reduced while the observed image becomes bright as the aperture diaphragm is increased. However, changes of the light amount accompanying such a decrease or increase lead to disadvantages for an observer.
The present invention has an object of providing an illumination apparatus for a microscope which improves prevention of dazzling when switching the objective lens or when switching the aperture diaphragm or when switching the observation method, with a simple structure.
An illumination apparatus of the present invention used for a microscope to guide illumination light to an objective lens attached to a revolving nosepiece comprises a light source for radiating the illumination light, an optical system for guiding the illumination light radiated from the light source, to the objective lens, an aperture diaphragm switching section provided in the optical system and having a plurality of aperture diaphragms and a light shielding portion, for switching the aperture diaphragm on the illumination light, linked with motion of the revolving nosepiece, when switching an observation method or the objective lens, and a control circuit for controlling operation of at least one of the aperture diaphragm switching section and the revolving nosepiece such that amount of light entering into the objective lens is prevented from undesirably increasing, when the observation method or the objective lens is switched.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.